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Deborah Estrin

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Sensor Network Tomography (Zhao, Govindan, Estrin) ... Sensor Network Tomography: Key Ideas and Challenges. Kinds of tomograms. network health ... – PowerPoint PPT presentation

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Title: Deborah Estrin


1
An Architecture for Sensor Networks Directed
Diffusion
  • Deborah Estrin
  • USC CS Dept and ISI
  • In collaboration with
  • Co-PIs Ramesh Govindan, John Heidemann
  • Diffusion Chalermak Intanagowat, Amit Kumar
  • Localized algorithms Jeremy Elson,Satish Kumar,
    Ya Xu, Jerry
    Zhao
  • Localization Lew Girod, Nirupama Bulusu
  • Distributed robotics Maja Mataric, Gaurav
    Sukhatme, Alberto Cerpa
  • For more information estrin_at_isi.edu

2
The long term goal
Embed numerous distributed devices to monitor and
interact with physical world in work-spaces,
hospitals, homes, vehicles, and the environment
(water, soil, air)
Network these devices so that they can coordinate
to perform higher-level tasks. Requires robust
distributed systems of tens of thousands of
devices.
3
Overview of research
  • Sensor network challenges
  • One approach Directed diffusion
  • Basic algorithm
  • Initial simulation results (Intanagowat)
  • Other interesting localized algorithms in
    progress
  • Aggregation (Kumar)
  • Adaptive fidelty (Xu)
  • Address free architecture, Time synch (Elson)
  • Localization (Bulusu, Girod)
  • Self-configuration using robotic nodes (Bulusu,
    Cerpa)
  • Instrumentation and debugging (Jerry Zhao)

4
The Challenge is Dynamics!
  • The physical world is dynamic
  • Dynamic operating conditions
  • Dynamic availability of resources
  • particularly energy!
  • Dynamic tasks
  • Devices must adapt automatically to the
    environment
  • Too many devices for manual configuration
  • Environmental conditions are unpredictable
  • Unattended and un-tethered operation is key to
    many applications

5
Approach
  • Energy is the bottleneck resource
  • And communication is a major consumer--avoid
    communication over long distances
  • Pre-configuration and global knowledge are not
    applicable
  • Achieve desired global behavior through localized
    interactions
  • Empirically adapt to observed environment
  • Leverage points
  • Small-form-factor nodes, densely distributed to
    achieve Physical locality to sensed phenomena
  • Application-specific, data-centric networks
  • Data processing/aggregation inside the network

6
Directed Diffusion Concepts
  • Application-aware communication primitives
  • expressed in terms of named data (not in terms of
    the nodes generating or requesting data)
  • Consumer of data initiates interest in data with
    certain attributes
  • Nodes diffuse the interest towards producers via
    a sequence of local interactions
  • This process sets up gradients in the network
    which channel the delivery of data
  • Reinforcement and negative reinforcement used to
    converge to efficient distribution
  • Intermediate nodes opportunistically fuse
    interests, aggregate, correlate or cache data

7
Illustrating Directed Diffusion
Setting up gradients
Source
Sink
8
Local Behavior Choices
  • 1. For propagating interests
  • In our example, flood
  • More sophisticated behaviors possible e.g. based
    on cached information, GPS
  • 2. For setting up gradients
  • Highest gradient towards neighbor from whom we
    first heard interest
  • Others possible towards neighbor with highest
    energy
  • 3. For data transmission
  • Different local rules can result in single path
    delivery, striped multi-path delivery, single
    source to multiple sinks and so on.
  • 4. For reinforcement
  • reinforce one path, or part thereof, based on
    observed losses, delay variances etc.
  • other variants inhibit certain paths because
    resource levels are low

9
Initial simulation studies(Intanago, Estrin,
Govindan)
FLOODING
  • Compare diffusion to a)flooding, and b)centrally
    computed tree (ideal)
  • Key metrics
  • total energy consumed per packet delivered
    (indication of network life time)
  • average pkt delay

DIFFUSION
CENTRALIZED
CENTRALIZED
DIFFUSION
FLOODING
10
What we really learnt (things we dont usually
showbecause in retrospect they seem so obvious)
  • IDLE time dominates energy consumptionneed low
    duty cycle MAC, driven by application.
  • With 802.11ish contention protocols you might as
    well just FLOOD
  • Easy to get lost in detailed simulations but in
    the wrong region of operation
  • Node density, traffic load, stream length, source
    and sink placement, mobility, etc.

11
Exploring Diffusion
  • Aggregation
  • Adaptive Fidelity
  • Implications
  • address free architecture
  • Need for localization
  • Using diffusion
  • System health measurements
  • Robotic nodes

12
Diffusion based Aggregation(Kumar, Kumar,
Estrin, Heidemann)
  • Scaling requires processing of data INSIDE the
    net
  • Clustering approach
  • Elect cluster head (various promotion criteria)
  • Aggregation or Hashing (indirection) to map from
    query to cluster head
  • Opportunistic aggregation
  • Reinforce (request gradient) proportional to
    aggregatability of incoming data (Amit Kumar)

13
Adaptive Fidelity(Xu, Estrin, Heidemann)
  • In densely deployed sensor nets, reduce duty
    cycle engage more nodes when there is activity
    of interest to get higher fidelity
  • Adjust node's sleeping time according to the
    number of its neighbors.
  • Initial simulations applied to ad hoc routing
  • Performance Metric Percentage of survived nodes
    over time.
  • The more nodes survive, the longer network
    lifetime

14
Comparison Density factor
  • At the left, from top to the bottom Adaptive
    Fidelity, Basic algorithm, regular AODV
  • Simulation under 50 nodes, 100 nodes, 150 nodes
  • Network lifetime is extended by deploying more
    nodes only with adaptive fidelity algorithm
  • Simulations available (ns-2 based)

15
Comparison Traffic Factor
  • At the left, from top to the bottom Adaptive
    Fidelity, Basic algorithm, regular AODV
  • Simulation under different traffic load 5pkt/s,
    10pkt/s, 15pkt/s, 20pkt/s
  • Longer network lifetime in adaptive
  • The more traffic load, the greater the advantage
    in terms of network lifetime

16
Adaptive Fidelity conclusions
  • Must be applied at application level (because
    just listening/having radio on dominates energy
    dissipation)
  • Unfortunate side effect of resource constraints
    is the need to give up (some) layering
  • Many open questions as to density thresholds and
    how to design algorithms to exploit it.

17
Implications local addresses?
  • Sensor nets maximize usefulness of every bit
  • each bit transmitted reduces net lifetime
  • cant amortize large headers for low data rates
  • underutilized address space is bad
  • Still need to identify transmitter
  • Reinforcements, Fragmentation
  • Use small, random transaction identifiers
    (locally selectedlike multicast addresses)
  • Treat identifier collisions as any other loss
  • Address-free method can win in networks with
    locality
  • simultaneous transactions at any one point is
    much less than in network as a whole

18
  • No need for global address assignmentbut how
    inefficient is it?
  • AFA optimizes number of bits used per packet
  • o Fewer bits less overhead per data bit
  • o More bits less contention loss

Efficiency of AFA as a function of local address
size.
19
Implcations Need Localization(Bulusu, Girod)
  • Many contexts you cant have GPS on every node
  • form factor
  • energy
  • obstructions
  • Beacon architecture
  • Signal strength alone problematic/hopeless
  • Federated coordinate systems
  • Acoustic ranging (client node asks beacons to
    send chirp and monitors time of flight)
  • Self-configuring beacon placement using robotic
    nodes

20
Localization is a critical service(Girod)
  • Devices take up physical space
  • Sufficiently fine-grained spatial coordinates
    provide implicit routing information (e.g.
    directing interests)
  • Location is relevant to many applications
  • Devices are doing things in the world users need
    to find them inputs and outputs to tasks often
    reference locations
  • How can we achieve fine-grained localization?
  • Need sensors to measure distance (ranging)
  • Time arrivals of 3 requested acoustic signals
    not signal strength
  • Relative or Global?
  • Relative spatial measurements more accurate
    because observed phenomena are local, shorter
    ranges, etc.
  • Global measurements (e.g. GPS) coarser (40m) but
    provide single coordinate system that can be
    exported unambiguously
  • Combine global scope of GPS with precision of
    relative sensors fuse local global coordinate
    frames

21
Localization relies on beacons(Bulusu,
Heidemann, Estrin)
  • Precision of localization depends on beacon
    density/placement
  • Uniform placement not good solution in real
    environments
  • Obstacles, walls, etc prevent inference based on
    signal strength/proximity detection
  • Self-configuring beacon placement is interesting
    application for robotic nodes
  • Given obstacles, unpredictable propagation
    effects, need empirical placement

22
Sensor Network Tomography(Zhao, Govindan, Estrin)
  • Continuously updated indication of sensor network
    health
  • Useful for
  • performance tuning
  • adjusting sensing thresholds
  • incremental deployment
  • refurbishing sections of sensor field with
    additional resources
  • self testing
  • validating sensor field response to known input

Tomogram indicating connection quality
23
Sensor Network Tomography Key Ideas and
Challenges
  • Kinds of tomograms
  • network health
  • resource-level indicators
  • responses to external stimuli
  • Can exchange resource health
  • during low-level housekeeping functions
  • such as radio synchronization
  • Key challenge energy-efficiency
  • need to aggregate local representations
  • algorithms must auto-scale
  • outlier indicators are different

24
Self configuring networks using and supporting
robotic nodes(Bulusu, Cerpa, Estrin, Heidemann,
Mataric, Sukhatme)
  • Robotics introduces self-mobile nodes and
    adaptively placed nodes
  • Self configuring ad hoc networks in the context
    of unpredictable RF environment
  • Place nodes for network augmentation or formation
  • Place beacons for localization granularity

25
CONCLUSIONS
  • Have just scratched the surface
  • We need to put more experimental systems in place
    and start living in instrumented environments or
    we risk too many rat-holes and pipe-dreams
  • Long-term and High-impact opportunities
  • Biological monitoring
  • Environmental sensing
  • Medical applications based on micro and nano
    scale devices
  • In-situ networks for remote exploration
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